etcdserver/etcdhttp: use MergeLogger to log etcdserver errors

Related https://github.com/coreos/etcd/issues/3812.

etcdserver/etcdhttp/client.go

@@ -605,9 +605,9 @@ func writeKeyError(w http.ResponseWriter, err error) {
 	default:
 		switch err {
 		case etcdserver.ErrTimeoutDueToLeaderFail, etcdserver.ErrTimeoutDueToConnectionLost:
-			plog.Error(err)
+			mlog.MergeError(err)
 		default:
-			plog.Errorf("got unexpected response error (%v)", err)
+			mlog.MergeErrorf("got unexpected response error (%v)", err)
 		}
 		ee := etcdErr.NewError(etcdErr.EcodeRaftInternal, err.Error(), 0)
 		ee.WriteTo(w)

etcdserver/etcdhttp/http.go

@@ -26,6 +26,7 @@ import (
 	"github.com/coreos/etcd/etcdserver"
 	"github.com/coreos/etcd/etcdserver/auth"
 	"github.com/coreos/etcd/etcdserver/etcdhttp/httptypes"
+	"github.com/coreos/etcd/pkg/logutil"
 )
 
 const (
@@ -35,6 +36,7 @@ const (
 
 var (
 	plog      = capnslog.NewPackageLogger("github.com/coreos/etcd", "etcdhttp")
+	mlog      = logutil.NewMergeLogger(plog)
 	errClosed = errors.New("etcdhttp: client closed connection")
 )
 
@@ -60,9 +62,9 @@ func writeError(w http.ResponseWriter, r *http.Request, err error) {
 	default:
 		switch err {
 		case etcdserver.ErrTimeoutDueToLeaderFail, etcdserver.ErrTimeoutDueToConnectionLost, etcdserver.ErrNotEnoughStartedMembers:
-			plog.Error(err)
+			mlog.MergeError(err)
 		default:
-			plog.Errorf("got unexpected response error (%v)", err)
+			mlog.MergeErrorf("got unexpected response error (%v)", err)
 		}
 		herr := httptypes.NewHTTPError(http.StatusInternalServerError, "Internal Server Error")
 		if et := herr.WriteTo(w); et != nil {